The good news first.
I'm informed that Brandin's bust in division 91 of Pere Lachaise has been removed by the conservation for safekeeping; unfortunately Lemaitre's bust in division 28 of Montmartre was solen sometime in late 2006.
It's still unclear to me why these thefts have happened. One theory is to melt down the bronze (the busts and medallions are all bronze apparently), and of course I suppose there might be a market for these things somewhere -- but where?
Questions I imagine the Paris police are asking right about now.